News of the 26-year-old's new contract follows his winning goal in Saturday's victory over St Mirren.
Millar told his club's official website: "I was delighted when the gaffer came to me and asked me to extend my stay and I am grateful to the club.
"The manager recently committed himself to an extended stay and Jody (Morris) has done the same and I am delighted to be the next to do so."
Boss Derek McInnes added: "I'm delighted to have Chris committed to the club in this way and he has earned that stability.
"He played a big part in getting us into the SPL and is already contributing to the task of keeping us there.
"Every club needs a player like Chris."